The present invention relates to a shielded heating lamp unit having a shield for use in protecting quartz or quartz-type lamps from damaging contaminants. More particularly, the present invention relates to a transparent tubular sheath of high temperature resistant material, such as for example quartz, within which a complementary-shaped quartz lamp is suspended in concentric spaced relationship to the inner walls of the sheath. The sheath permits handling of the quartz lamp without fear of depositing splatter and or contaminants, etc. on the lamp's outer surface and, more importantly, permits the quartz-type lamp to be used as an element in a heating device, such as for example a heating device for cooking and/or broiling foods.
Quartz-type lamps generate substantial amounts of heat and are typically useful for heating and lighting purposes. A typical quartz-type heat lamp can generate up to 4500.degree. Fahrenheit and develop from 300 to 5000 watts with an efficiency of 93%. This heat is almost instantly generated after the lamp is energized. However, quartz-type lamps are easily damaged by the deposit of contaminants on the lamp's surface which limits their usefulness.
In most cases, Nichrome wire elements in a metal sheath are generally used in heating and cooking applications. Some elements are formed by inserting a section of nichrome wire into an outer metal casing and then packing the casing with magnesium oxide to insulate the wire from the casing. The unit is then swedged through a machine to approximately 3/8 inch to 3/8 inch in diameter. This compresses the casing and insulating material about the wire. Other methods of using bare Nichrome wires for heating elements have limitations also. The wire is dangerous and caution must be used to prevent being burnt or electrocuted.
Nichrome wire elements only generate approximately 1600.degree. Fahrenheit with an efficiency of approximately 43%. Further, there is a considerable time lag to peak temperature when compared to the quartz-type lamp which is almost instantaneously develops peak temperature. When compared, a quartz-type lamp is greatly superior to the nichrome wire element in heating and cooking applications. The major problems with quartz-type lamps is their sensitivity to contaminants and extreme fragility.
When using quartz-type lamps, special care must be exercised to prevent deposits on the lamp's outer surface. Generally, clean cotton gloves or other protective means must be used when handling the lamps to prevent oil or grease from the person's hands from being deposited on the lamps. Deposits of oil, grease, or other contaminants on the lamp's outer surface can substantially reduce the lamp's life. For example, a typical quartz lamp may operate for approximately 5000 hours at rated voltages if it is handled properly. Should the surface of the quartz lamp be contaminated, it may last for a substantially less useful life.